A transmission device for an access network, for example a Distribution Point, may be reverse-powered from the customer premise equipment (CPE), thereby avoiding the need of a connection to the electrical network. The wire line between the Distribution Point and the CPE may be shared by a data service and a telephone service (POTS for plain old telephone service), for example.
The DC component of the POTS signal needs to be blocked to avoid conflict with the reverse power provided by the CPE. However, the DC component of the POTS should not be blocked when the Distribution Point is not powered from CPE, for example in case of power failure at the customer premises, so as to allow continuity of the POTS. For this purpose, the Distribution Point may include a lifeline relay having an open state wherein the DC component of the POTS signal is blocked and a closed state wherein said DC component is not blocked.
In that case, before starting the reverse power, it is necessary to switch the lifeline relay from the closed state to the open state. This requires power, which may be provided by batteries. However, batteries need maintenance, have to be replaced after some time, and are only operational in a limited temperature range.